This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Osteogenesis imperfecta is an inherited autosomal dominant disorder of type I collagen characterized by multiple fractures and bone fragility fractures. OI affects approximately 1 to 2 out of every 10,000 individuals of all racial and ethnic origins. There is no cure for osteogenesis imperfecta, and there is no established medical therapy for adults with the disorder. The purpose of this study is to determine the effectiveness of teriparatide (FORTEO) for increasing bone mass and improving bone structure in adults affected with osteogenesis imperfecta (OI). There are no data concerning the usefulness of parathyroid hormone (PTH) therapy in OI. An effective anabolic therapy available for the treatment of adults patients with OI would be an extremely attractive and valuable asset not only to the affected patients but also to the medical community at large. The working hypothesis is that individuals affected with OI who are treated with teriparatide will experience increased spine and femoral neck mineral density and improvements in bone geometry (an increase inbone width and cortical thickness). The underlying pathophysiology of OI is a quantitative or qualitative abnormality in the synthesis of type I collagen, the most abundant protein in bone. Although teriparatide is not expected to change the defect in the collagen produced, it is expected to increase the quantity of bone formed. Therefore, we hypothesize that by increasing bone mineral density, overall bone strength will be enhanced in OI and fracture incidence will be reduced. The primary outcome variable will be BMD, but a variety of other variables will also be assessed including serum and urine markers of bone remodeling, quantitative computed tomography (QCT) measures of bone structure and safety parameters. DNA will be collected for possible future analyses. Patients with OI will be enrolled in this study for about 18 months. Half the patients will receive PTH (FORTEO) and the other half placebo. Blood, urine, and bone density tests will be done during the study for monitoring safety and to determine the efficacy of PTH.